Use of powerlines for transmission of high frequency signals

ABSTRACT

Communication is provided which includes receiving a transmitted radio signal at a powerline wherein the powerline functions as a receiving antenna for the wirelessly transmitted radio signal. The powerline is coupled to an input of a radio receiver using a coupler to communicate the radio signal to the radio receiver. For calibration purposes a second antenna not coupled to powerline may be used. A method for powerline communication across transformers, open circuit breakers, and other devices is also provided. In addition, a method of monitoring a device connected to a powerline is provided.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Divisional Application of U.S. Ser. No. 12/048,820filed Mar. 14, 2008, which claims priority under 35 U.S.C. §119 toprovisional application Ser. No. 60/894,756 filed Mar. 14, 2007, hereinincorporated by reference in their entirety.

GRANT REFERENCE

This application was made with Government support under ContractsW31P4Q-05-C-R067 and W31P4Q-06-C-0221, awarded by the U.S. Army Aviationand Missile Command. The Government has certain rights in the invention.

BACKGROUND OF THE INVENTION

The present invention relates to the use of powerlines for transmissionof high frequency signals. More particularly, but not exclusively, thepresent invention relates to the use of powerlines: in wirelesscommunications where the powerlines are used as antenna; thecommunication of signals across transformers, open circuits or otherdevices associated with powerlines; and monitoring powerline noise todetermine information about devices connected to a powerline. To assistin explanation of the present invention, problems associated withpowerlines are discussed. Such problems may seem unrelated, without thebenefit of this disclosure.

Generally, it is known to use powerlines for communications, such as maybe used for home networking or other purposes. In such a network,computers or other network devices are interfaced to an outlet of thepowerline and communications signals are sent over the power line. Thepowerline signals typically have a frequency of 60 Hz so a high passfilter can be used to filter out the 60 Hz. The communications signalssent over the power line are substantially higher such as on the orderof 4 to 24 MHz. U.S. Pat. No. 6,243,413 to Beukema discloses one suchexample of using powerlines for communications. Various HomePlug®devices exist from multiple manufacturers. One problem exhibited byvarious examples of such devices is that such devices do not demonstrateadequate surge survivability. U.S. Pat. No. 6,130,896 to Luker et al.discloses another example of such a use of powerlines forcommunications. Luker et al. further discloses that a device connectedto the powerlines may also be connected to an access point with anantenna for providing wireless communication.

Another problem related to communications over powerlines is the effectof open circuits, equipment such as transformers, or other devices orsignals transmitted across the powerlines. Communications overpowerlines may not be viable in certain applications unless effects ofopen circuits, equipment such as transformers, or other devices can bemanaged.

A seemingly unrelated problem is failure of devices connected to powerlines, such as, but not limited to, transformers. Failure of suchdevices may result in disruptions of service. It would be advantageousif failure of such devices could be predicted prior to its occurrence sothat devices could be repaired or replaced prior to failure.

Another seemingly unrelated problem relates to worker safety in largestructures and mines. In the event of a disaster such as a structuralfailure or mine cave-in, locating workers as expeditiously as possiblebecomes a primary concern. Yet doing so can be difficult for a varietyof reasons and presents a more complex set of problems than is presentin other location finding applications. For example, services such asGPS are not options because the workers within certain structures,especially metal structures or workers who are underground have noline-of-sight to either GPS satellites or other workers. Radio signalsbecome highly attenuated which makes it impractical to use conventionalapproaches. What is needed is a way to locate workers trapped within alarge structure or in a mine.

BRIEF SUMMARY OF THE INVENTION

It is a primary object, feature, or advantage of the present inventionto improve over the state of the art.

It is a further object, feature, or advantage of the present inventionto use powerlines as antenna in wireless communication.

It is a still further object, feature, or advantage of the presentinvention to provide for a means of calibrating for different powerlinenetworks.

Yet another object, feature, or advantage of the present invention is toprovide a device that interacts with powerlines and provides adequatesurge survivability.

A still further object, feature, or advantage of the present inventionis to provide a method for powerline communication across transformers,open circuit breakers, and other devices.

Yet another object, feature, or advantage of the present invention isthe characterization of devices connected to a power-line using ananalysis of high frequency impedance.

Another object, feature, or advantage of the present invention is toassess the reliability or state of a transformer or other powerlineequipment.

One or more of these and/or other objects, features, or advantages ofthe present invention will become apparent from the specification andclaims that follow.

Wireless communication may occur using the powerlines as one orpotentially more than one antenna over both conventional powerlinecommunication frequencies, and much higher frequencies (includingfrequencies above 100 MHz) using either conventional radio, softwaredefined radio and either conventional or subsampling receptiontechniques. Furthermore, wireless nodes and wired nodes may interoperatewith each other using potentially the same signaling methods.

According to one aspect of the present invention a method of wirelesscommunication is provided. The method includes receiving a wirelesslytransmitted radio signal at a powerline wherein the powerline functionsas a receiving antenna for the wirelessly transmitted radio signal. Themethod further includes coupling the powerline to an input of a radioreceiver using a coupler to communicate the radio signal to the radioreceiver. The coupler provides for blocking the alternating currentpower signal while limiting radio frequency loss and providing surgeprotection. The method may further include sending a second radio signalfrom a radio transmitter through the coupler and to the powerlinewherein the powerline functions as a sending antenna for the secondradio signal. The method may further include calibrating the radioreceiver for use with the powerline by comparing performance of thepowerline with a second antenna.

According to another aspect of the present invention a system isprovided. The system includes a radio receiver having an input, anoptional power attenuator electrically connected to the radio receiverinput and a line coupler electrically connected to the power attenuatorand to a power line, the power line providing an alternating currentline level voltage and wherein the powerline functions as an antenna forthe radio receiver. The optional power attenuator may be used formeasuring the S-parameters of the power-line unless there is also atransmit/receive (T/R) switch or other means of changing the attenuationsuch that the attenuation is at a minimum when the system is listeningto a remote transmitter. The system may further include a radiotransmitter having an output and a power amplifier electricallyconnected to the output of the radio transmitter and the line couplerand wherein the power line function as an antenna for the radiotransmitter. The radio receiver may further include a second input andan antenna electrically connected to the second input of the radioreceiver to thereby provide data for use in calibration or otherpurposes.

According to another aspect of the present invention, a system isprovided. The system includes a radio transmitter having an output, anda line coupler electrically connected to the transmitter output and to apower line, the power line providing an alternating current line levelvoltage and wherein the powerline functions as an antenna for the radiotransmitter.

According to another aspect of the present invention, a method forpowerline communication across transformers, open circuit breakers, andother devices is provided. The method includes providing a signal at asignal output, the signal at a frequency selected to reduce loss over acommunication path that includes one or more transformers or opencircuit breakers, coupling the powerline to the signal output at a firstlocation using a coupler to communicate the signal over the powerline,and receiving the signal at a second location, the second locationseparated from the first signal by the communication path.

According to another aspect of the present invention, a method ofmonitoring a device connected to a powerline is provided. The methodincludes monitoring powerline noise across the power line and analyzinghigh frequency impedance associated with the powerline noise todetermine information about the device.

According to another aspect of the present invention, a method forenhancing worker safety is provided in large structures and mines. Themethod includes equipping a worker with a beacon device, the beacondevice adapted for wirelessly communicating a beacon signal identifyingthe beacon device or the worker. The method further includes receivingthe beacon signal at a powerline wherein the powerline functions as areceiving antenna for the beacon signal and coupling the powerline to aninput of a radio receiver using a coupler to communicate the beaconsignal to the radio receiver. The method also provides for determininglocation of the beacon device at least partially based on the beacondevice.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a block diagram illustrating use of powerlines in wirelesscommunications.

FIG. 1B is a block diagram illustrating one embodiment of a system usingpowerlines in wireless communications.

FIG. 2 is a chart illustrating measured transmission (S₂₁) from thepower line to an ˜3 ft. antenna placed within the room.

FIG. 3 is a chart illustrating measured wireless transmission (S₂₁) fromthe power line in an outbuilding.

FIG. 4 illustrates captured spectrum near 100 MHz (subsampled) using anexternal antenna.

FIG. 5 illustrates captured spectrum near 100 MHz (subsampled) using aline coupler plugged into the power line.

FIG. 6 is a schematic of one embodiment of a powerline coupler.

FIG. 7 illustrates measured S₂₁ and S₁₁ magnitudes for one embodiment ofa powerline coupler.

FIG. 8 is a schematic of an alternate embodiment of a powerline coupler.

FIG. 9 is a schematic of another alternate embodiment of a powerlinecoupler.

FIG. 10 is an illustration of one embodiment of a device with modular ACor RF connectors.

FIG. 11 is a graph illustrating the magnitude S21 response of a simple15 Amp breaker shown for ON and OFF settings

FIG. 12 is a graph illustrated measured receive power for a 10 dBmin-phase transmitter.

FIG. 13 is a graph of the magnitude of the forward S parameters from oneprimary to each of three secondary coils for a power transformer.

FIG. 14 provides a block diagram illustrating a beacon

FIG. 15 illustrates a signal wirelessly transmitted to a receiver placedon a powerline.

FIG. 16 illustrates a signal wirelessly transmitted to a receiverunplugged from the powerline.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention provides for wireless communications to occurusing powerlines as one or potentially more than one antenna over bothconventional powerline communication frequencies, and much higherfrequencies, above 100 MHz using either conventional radio, softwaredefined radio and subsampling reception techniques. Furthermore,wireless nodes and wired nodes may interoperate with each other usingpotentially the same or alternate signaling methods.

FIG. 1A provides a block diagram illustrating the use of powerlines incommunications. A transmitter 11 is coupled to powerlines 38 and areceiver 13 is coupled to power lines 38. An output 12 is electricallyconnected to a power amplifier 20. The power amplifier 20 iselectrically connected to a line coupler 32 which is coupled to thepower lines. The coupler 32 may also be electrically connected to anoptional impedance 34. In the receiver 13, the powerlines 38 areelectrically coupled to a line coupler 32 which may be electricallyconnected to an optional impedance 34. The line coupler 32 iselectrically connected to an input 16 of the receiver 13.

FIG. 1B illustrates one embodiment of a system 10 which uses powerlinesin communications or for measuring characteristics of devices attachedto the powerlines. As shown in FIG. 1B, system 10 associated with asoftware defined radio system (SDR) Universal Software Radio Peripheral(USRP) is provided. The USRP is one example of a high speed USB basedboard for making software radios and is available from Ettus ResearchLLC. The radio used need not be a software radio. A USRP or lowfrequency transmitter (LFTX) output 12 is shown. The USRP/LFTX output 12is electrically connected to an amplifier such as a 30 dB poweramplifier 20. The 30 dB power amplifier 20 is electrically connected toa splitter 28, which splits the signal into a first output, A, and asecond output, B. The second output B, is electrically connected to anattenuator such as a 30 dB power attenuator 22 which is electricallyconnected to a USRP or basic receiver input 14. The first output A fromthe splitter 28 is electrically connected to a directional coupler 30.The directional coupler is electrically connected to a 40 dB powerattenuator 24 which is electrically connected to a USRP or basicreceiver input 16. The directional coupler 30 is also electricallyconnected to a line coupler 32. The line coupler 32 is electricallyconnected to an impedance 34 of approximately 50 ohms or may alternatelybe connected to a receiver input, such as block 18 or may be left open.The line coupler 32 is coupled to a power line 38. One or more variableline devices 36 may be electrically connected to the power line 38.Thus, the powerline 38 may be used as an antenna coupled to the system10 shown. In addition the powerline is used in its conventional manner,namely to provide alternating current at or near a standardized voltagelevel and at or near a standardized frequency. One example of such astandardized voltage level is 120 VAC operating at 60 Hz. Of course,such a voltage level is approximate only and may vary somewhat as iswell known in the art.

A second receiver input 18 is also shown. The second receiver input 18is electrically connected to an antenna 26. Different powerline networksin different buildings or buildings type may exhibit differences inbehavior for various reasons. As will later be explained in more detail,the antenna 26 may be used in the system 10 to provide assistance incalibrating the system 10 or for other purposes.

The configuration of FIG. 1B provides for a software defined radiosystem (SDR) Universal Software Radio Peripheral (USRP) system with adirectional coupler and splitter to perform the vector network analysis(VNA) function whereby the characteristic impedance and scatteringparameters of the power line may be measured. The present invention hasalso obtained transmission via an antenna that is placed within the sameroom as the line coupler. Comparing measurements of when the receiverconnection was open and those where it was attached to the antenna, onecan infer the actual wireless transmission between the power line andthe freestanding antenna.

Examples of wireless measurements taken with this setup are shown inFIG. 2 and FIG. 3 for two different buildings at a location north ofAmes, Iowa USA. Note that both plots include data with open antennaconnections so as to infer coupling from board or chip level crosstalkthat is very small relative to the received signals. For somefrequencies the magnitude of coupling via the antenna is comparable tothat with an additional line coupler. Thus, wireless mesh nodes could beinterspersed with wired nodes, should the usual electrical connectionnot be possible or desirable. The USRP VNA function is limited to about30 MHz but we have noticed that wireless coupling on and off thepowerlines is significant at even commercial FM frequencies includingthose over 100 MHz. The USRP can receive these frequencies using a BASICRX front-end (with no anti-aliasing filter) and using the A/D in asub-sampling mode. The BASIC RX is one example of a daughterboardavailable for USRP. Hence, data can be received from even sub-carriersriding along with commercial FM broadcasts. Examples of FM bandreception are shown in FIG. 4 and FIG. 5. For FIG. 4 the same broadbandantenna used for FIG. 2 and FIG. 3 was used, but now the USRP was tunedto around 100 MHz (subsampled). In FIG. 5, the antenna was replaced witha line coupler revealing much of the same spectral structure.

As shown in FIG. 1B, the line coupler 32 is coupled to a power line 38.Coupling of RF signals on or off the power-lines must be done in such away so as to block the 120 VAC present on the lines but also minimize RFloss. This is particularly challenging because the coupler must alsoperform a surge protection function that must minimize the impact oflightning induced or other transients from significantly disruptingcommunications or damaging equipment. For particularly long-terminstallations, the importance of adequate surge survivability is clearlyimportant, and is reportedly a significant shortcoming of somecommercial HomePlug® devices. Attenuation may be performed byattenuators. The attenuation is primarily used to protect it from alocal transmitter. Instead of a power attenuator between the linecoupler and the receiver input a transmit/receive (T/R) switch may beused or other means of changing the attenuation such that attenuation isat a minimum when the system is listening to a remote transmitter. Onemay want to attenuate when the local transmitter is operating,especially if there is a power amplifier present which may damage thereceiver.

Several variations of couplers were designed and prototyped with oneversion being shown in the schematic of FIG. 6. Earlier prototypes hadused more traditional surge protectors including MOV devices and/orsilicon chip or discrete Schottky diodes but all of these methodsexhibited an unacceptable frequency response with dips in the frequencyresponse of 30 dB or more below 100 MHz. In contrast, the unit shown inFIG. 6 is useful to beyond 150 MHz and shows only a few dB of loss tobeyond 100 MHz. First order surge protection is provided via a pair ofpositive temperature coefficient high voltage thermistors and lowcapacitance gas discharge units (Bourns miniature 3-pole 230V dischargetubes that contain 2 tubes in one enclosure) that return to the circuitground connection. During power surges, these discharge tubes turn onand maintain the voltage across them to below about 300 V and canmomentarily absorb several thousand Amps. Any heating of the thermistorsduring a surge or other longer term anomalous high voltage event raisesthe thermistor resistance, further protecting the circuit. The voltageat the surge protectors is passed through a pair of high voltagecapacitors to the primary of a high-frequency transformer. Thesecapacitors were problematic in our prototypes as many high voltagecapacitors do not exhibit acceptable behavior at high frequencies. Weused polypropylene capacitors because they usually display a low losstangent but we ultimately had to hand select part types based uponexperimental measurements of the individual capacitors. We ultimatelyused 1600V (or higher) parts such as those available from BC Componentsin sizes of between 1 and 10 nF for our prototypes. The Minicircuits RFtransformer (ADTT1-1) was a manufactured unit that was selectedprimarily for its frequency response range (<2 dB from 0.4-200 MHz) andthe availability of center taps. It is adequate for both receiving andsending at less than 0.25 Watt but may be replaced for a more robustunit with higher power capability.

The secondary coil of the transformer is tied to a low capacitance (2pF) transient voltage suppressor or TVS (Diodes Incorporated DLP05LC)that uses a fast responding diode and is biased off by a 3V local powerconnection (2 AA cells). This surge suppressor can momentarily shuntover 10 Amps which exceeds what we believe to be the likely maximumsecondary surge current from the transformer. Finally, a ⅛ Amp microwavefuse is in series with the 50 Ohm BNC output connection that is floatingrelative to the primary or input ground connection. Although the circuitshown in FIG. 6 is functional, it has been found that in someimplementations it may be difficult to locate adequate PTCs and using asimple resistor may result in a blown resistor (as later explained,placing a second set of capacitors to the left of the discharge tubeappears to resolve any failure issues).

Measured S₁₂ and S₁₁ parameters for this coupler are shown in FIG. 7.Note that for measurement of component S-parameters that are measuredthrough the couplers, the coupler response is calibrated out. This isaccomplished by performing short, open and through calibrations on theremote side of each coupler.

An alternate circuit embodiment is shown in FIG. 8 where no gasdischarge components are used but instead where surge protection isprovided by bidirectional low capacitance semiconductor devices. In bothembodiments shown in FIG. 7 and FIG. 8, surge protection of thetransformer is enhanced by floating the transformer winding coupled tothe power line between a pair of high voltage capacitors.

Another alternative circuit embodiment is shown in FIG. 9. The circuit100 includes a high voltage area 101. Within the high voltage area 101is a connector 102 for the line, neutral, and ground. Sub circuits 106,108 are shown. A gas discharge tube 104 is provided between the subcircuits. An optional MOV 110 is shown which may be used in place of thegas discharge tube. MOVs are generally less expensive than gas dischargetubes but have a higher parasitic capacitance and hence may not beusable at higher frequencies of use. A fuse 112 is provided to furtherprotect the circuit. A resistor 114 and high voltage capacitors 116, 118are shown. The gas discharge tube 104 limits the voltage across thetransformer primary 124 and the high voltage capacitors 116, 118connections without shorting the AC line. The gas discharge tube 104 ismore likely to survive large surges than alternatives such as placing anMOV across the powerline. A fast semiconductor suppression device 120 isprovided across the primary winding 124 of the transformer 122. Thecircuit 100 also includes internal bleed resistors in the sub circuits106, 108 and resistor 114 which will remove charge from the capacitorswhen the circuit is unplugged from the wall and thereby preventaccidental discharge of the capacitors. The circuit 100 as shownillustrates multiple transformer secondary windings. Two are shown, butadditional windings may be used. For explanation purposes, the primary124 is the windings towards the AC line and the secondary are thewindings 126, 128 towards the SMA connectors 138, 140. Instead of SMAconnectors, a coax connection or other type of connection may be used.The circuit 100 may be programmed to connect to either the line voltageand neutral or the line voltage and ground. One or the other may be moreeffective.

A further improvement on this scheme would be to have a ‘clip-on’ ACplug similar to that employed on the Linksys PAP2-NA AC adapter butwhere another clip-on module would consist of a BNC or other common RFplug-type that would allow for very simple calibration of the unit inthe field. For example, instead of having a length of AC power cord,make the AC plug assembly modular with a BNC module that would attach tothe same portal. There would then be no issue of calibration errorsbecause of the short length of line cord (there would be none) andcalibration would be very straightforward via the modular BNC connector.FIG. 10 illustrates one such embodiment of such a device 50 where amodular BNC connector 54 (or other RF connector) may be snapped off andan AC compatible plug 56 snapped on. The device 50 includes an RFinput/output 52 such as a BNC connector which may be mounted to the caseor housing of the device 50. The modular BNC connector 54 and ACcompatible plug 56 may be interchanged with a BNC or other RF connectorfor purposes of calibration or other purposes.

The system of the present invention allows for powerlines to be used invarious ways. Power-lines may be used as communication medium for sensorrelated ad-hoc networks. The system may be used to operate across opencircuit breakers and switches, different phases of transformers and evenacross distribution transformers. The present invention provides forwireless communication where powerlines are used as antenna.Conventional powerline frequencies may be used as well at much higherfrequencies, including those over 100 MHz. In addition, it is to beunderstood that the present invention is not to be limited to a 120V, 60Hz system. Other types of systems are contemplated, including 240Vsystems, and 230V 50 Hz systems. Also, wireless nodes and wired nodesmay interoperate with each other using potentially the same signalingmethods. These and other variations, alternatives, and options arewithin the spirit and scope of the invention.

Method for Powerline Communication Across Transformers, Open CircuitBreakers, and Other Devices

Another aspect of the present invention relates to powerlinecommunication across transformers, open circuit breakers, and otherdevices. The present inventor has found that signaling in one or morebands of frequency exhibits relatively low loss on real systems.

The frequency response of both individual circuit breakers and powernetworks containing them was measured. For example, FIG. 11 illustratesthe magnitude S21 response of a simple 15 Amp breaker shown for ON andOFF settings. As is shown in FIG. 11, the difference between the ON andOFF responses is relatively small above about 100 MHz. Surprisingly, ina real network, this effect extends to much lower frequencies.Apparently because of radiated pickup within switchboxes and possiblytransmission via the neutral line, significantly greater coupling occursthan could be easily inferred from measurements of the individualbreakers. As an example of this, measured receive power for a nearby 10dBm in-phase transmitter is shown in FIG. 12. Differences between thetwo curves are generally less than 10 dB above about 15 MHz! Thissuggests that optimal operating frequencies for systems that may haveopen circuit breakers are likely much lower than would be expected fromindividual breaker measurements as losses from power cables andtransformers are generally smaller at lower frequencies.

S-parameters have been measured for both pad and pole mounteddistribution transformers. Apparently because of internal capacitancebetween windings and internal resonances, there is considerabletransmission between phase terminals at some frequencies as shown inFIG. 13. Losses of as little as 10 dB are present at some frequenciesalthough passage through two transformers will usually be required. Thefrequency response of distribution cable (used between transformers) hasalso been evaluated and has been shown to exhibit relatively little lossin comparison with the low-voltage cabling used within buildings. Hence,signaling across these barriers must be able to accommodate anadditional 20+ dB of likely loss and be able to detect and use therelatively narrow resonant peaks.

One example, where communication needs to take place across multipletransformers is found in many large buildings. In such buildings,cascaded transformers are present. For example, one transformer may gofrom −13 kV to 480V and the second transformer may go from 480V to 120V.In such an instance communication across a 120V powerline may involvecommunication across two sets of the cascaded transformers. Of course,the present invention contemplates any number of combinations oftransformers, open circuits, or other devices that may be associatedwith a powerline.

Transformer Reliability Assessment via Broadband Power Line NoiseDetection

Insight into powerline noise has applications beyond communications. Onesuch application is assessment of transformer reliability usingbroadband power line noise detection. Degradation of a transformerdielectric is frequently characterized by low level arcing within thedielectric. This arcing is more prone to occur at times when thedielectric is stressed with a large potential placed across it. Thearcing itself results in emission of broadband noise that to some degreewill be transmitted to the primary and secondary feeds of thetransformer. Because the timing of the emission is generallysynchronized with the applied voltage, the noise due to this dielectricarcing may generally be separated from other broadband noise bycomparing the detected signal components when the voltages are neartheir peaks and when they are of a significantly different potential.Noise sources that are not synchronized with the power line will havevery similar signal powers during the two intervals. Differencing of RMSnoise powers during the two intervals should give an indication of therelative magnitude of line voltage induced arching. Furthermore, forthree phase transformers, the position of the failing dielectric may beinferred by the relative noise magnitudes as a function of where itoccurs during the 360 degree phase cycle.

Thus, an understanding of powerline noise allows one to determine theusefulness of equipment of this type in predicting transformer failuresbased upon detection of high frequency noise emissions that arecorrelated with the power line voltages. Changes in S-parametermeasurements over time may also be used for prediction of componentfailure if the pending failure or change in device characteristicsresults in a change in high frequency characteristics.

Beacon Using Powerline Antennas

By placing a small transmitter on a person or piece of equipment thattransmits in the few hundred kHz to perhaps ˜130 MHz, a signal that isunique to the person or equipment, the approximate location of thetransmitter may be inferred based upon the signal received through thepower line. This signal may be a periodically repeating beacon that onlyidentifies the transmitter number or may also contain environmental oruser entered data such as a text message. FIG. 14 provides a blockdiagram illustrating a beacon 150 with a transmitter 152. Thetransmitter is in an operative communication with a receiver 154 whichis connected to a power line 156 which acts as a receiving antenna.

An example of such as signal that was wirelessly transmitted to areceiver placed on the powerline is shown in FIG. 15. Here a 35 kb/swaveform using GMSK modulation is wirelessly transmitted at about 10 MHzto a receiver that is physically located some distance from thetransmitter using the AC powerline as a receiving antenna. Although GMSKmodulation is one type of modulation that may be used, other types ofmodulation as known in the art, may also be used.

The same signal with the receiver unplugged from the powerline is shownin FIG. 16. This signal is received via wireless transmission directlyto the receiver unit with no powerline component. As can be seen by thedifference between the two figures, the powerline significantly improvesthe signal reception. Thus, the present invention may be used in thecontext of receiving beacon transmissions and inferring information fromthe beacon transmissions, including location information. Informationsuch as location information may be inferred in the same mannerpreviously discussed in other applications by examining characteristicsof the signal. Other approaches may be used. One approach would be touse multiple receivers, for example on each power phase or powersegment. Each receiver could distinguish from which line the largestsignal was coming from. For example, if each tunnel near the end of themine had a receiver, one could determine which tunnel the beacon is in.Alternatively, several receivers may be placed in a line and one canlook for the strongest signal. A more sophisticated approach wouldactually use temporal information and relative time of arrival in orderto infer position. A third method would actually have the beacon act asa transponder that would transmit upon receiving an inquiry. In such anembodiment the beacon also contains a receiver. Of course, otherapproaches may be used. One example of where beacon based transmissionsmay be useful is underground, such as in mines.

One of the main advantages of using the powerline as a receiving antennais that most powerlines are mechanically very rugged and willpotentially survive structural collapses or failures in areas such asmines where the surrounding earth will largely preclude any directwireless transmission over any length. A local receiver unit could beplaced near the working areas of a mine and relay personnel or equipmentinformation to the surface using either conventional network methods orpowerline communications.

The present invention contemplates that various modulation schemes maybe used, although preferred modulation schemes include direct sequencespread spectrum (DSSS) or differential quadrature phase shift keying(DQPSK). Where DQPSK is used, the bandwidth used may be only a few MHzwide or less and need only use a single or a few tones.

Thus, the present invention has been disclosed, including its variousaspects relating to use of powerlines as antenna, communication overpowerlines, using powerline antennas to receive beacon signals, andusing high frequency impedance to determine information about devices onthe powerlines. The present invention contemplates numerous options,variations, and alternatives, and is not to be limited to the specificdetails of the embodiments set forth herein.

1. A method for powerline communication across transformers, open orclosed circuit breakers, and other devices, comprising: providing asignal at a signal output, the signal at a frequency higher than afrequency of the power line and selected to reduce loss over acommunication path traveling through one or more transformers or open orclosed circuit breakers; coupling the powerline to the signal output ata first location using a coupler to communicate the signal over thepowerline; receiving the signal at a second location, the secondlocation separated from the first signal by the communication path. 2.The method of claim 1 wherein the loss is less than about 30 dB.
 3. Themethod of claim 1 wherein the loss is than about 10 dB.
 4. The method ofclaim 1 wherein the frequency is at least 100 Hz.
 5. The method of claim1 wherein the one or more transformers or circuit breakers includes atleast two transformers.
 6. The method of claim 5 wherein the at leasttwo transformers comprises two cascading transformers.
 7. A method forenhancing worker safety, comprising; equipping a worker with a beacondevice, the beacon device adapted for wirelessly communicating a beaconsignal identifying the beacon device or the worker; receiving the beaconsignal at a powerline wherein the powerline functions as a receivingantenna for the beacon signal; coupling the powerline to an input of aradio receiver using a coupler to communicate the beacon signal to theradio receiver; and determining location of the beacon device at leastpartially based on the beacon signal.
 8. The method of claim 7 whereinthe coupler includes a surge protector.
 9. The method of claim 7 furthercomprising sending a second radio signal from a radio transmitterthrough the coupler and to the powerline wherein the powerline functionsas a sending antenna for the second radio signal.